import { useCallback, useEffect, useState } from 'react';
import { Archive, MessageSquare, RotateCcw } from 'lucide-react';
import { toast } from 'sonner';
import { ChatInput } from '@/components/ChatInput';
import { api } from '@/api/client';
import type { Chat } from '@/api/types';

interface Props {
  projectId: string;
  sessionId: string;
  agentId?: string | null;
  onAgentChange?: (agentId: string | null) => void | Promise<void>;
  onSend: (content: string) => void;
  // Slash-command (skill) send from the landing page. The parent creates the
  // chat, assigns it to the pane (so it transitions to ChatPane), and invokes
  // the skill — same transition the text send uses. See useSessionChats.
  onSkillInvoke: (skillName: string, userMessage: string | null) => void;
  createChat: () => Promise<{ id: string }>;
  // Session history: the session's open chats (live), and callbacks to open one
  // in THIS pane / restore an archived one. Archived chats are fetched here
  // (the default open-only list excludes them).
  chats: Chat[];
  onOpenChat: (chatId: string) => void;
  onUnarchiveChat: (chatId: string) => Promise<void>;
}

function formatRelative(iso: string): string {
  const then = new Date(iso).getTime();
  if (Number.isNaN(then)) return '';
  const s = Math.max(0, Math.round((Date.now() - then) / 1000));
  if (s < 60) return 'just now';
  const m = Math.round(s / 60);
  if (m < 60) return `${m}m ago`;
  const h = Math.round(m / 60);
  if (h < 24) return `${h}h ago`;
  const d = Math.round(h / 24);
  if (d < 7) return `${d}d ago`;
  return new Date(iso).toLocaleDateString();
}

function byRecent(a: Chat, b: Chat): number {
  return (b.updated_at ?? '').localeCompare(a.updated_at ?? '');
}

export function SessionLandingPage({
  projectId,
  sessionId,
  agentId,
  onAgentChange,
  onSend,
  onSkillInvoke,
  createChat,
  chats,
  onOpenChat,
  onUnarchiveChat,
}: Props) {
  const [chatId, setChatId] = useState<string | null>(null);
  const [archived, setArchived] = useState<Chat[]>([]);

  // Archived chats aren't in the default (open-only) list, so fetch them. One
  // shot on session change — the history view is transient (pick a chat and
  // it's gone), so slight staleness is fine; reopening the pane refetches.
  useEffect(() => {
    let cancelled = false;
    api.chats
      .listForSession(sessionId, { status: 'archived' })
      .then((list) => { if (!cancelled) setArchived(list); })
      .catch(() => {});
    return () => { cancelled = true; };
  }, [sessionId]);

  const ensureChat = useCallback(async (): Promise<string> => {
    if (chatId) return chatId;
    try {
      const chat = await createChat();
      setChatId(chat.id);
      return chat.id;
    } catch (err) {
      toast.error(err instanceof Error ? err.message : 'Failed to create chat');
      throw err;
    }
  }, [chatId, createChat]);

  const handleSend = useCallback(async (content: string) => {
    const text = content.trim();
    if (!text) return;
    try {
      await ensureChat();
      onSend(text);
    } catch {
      // Error already surfaced via toast.
    }
  }, [ensureChat, onSend]);

  // Route to the parent, which creates the chat, assigns it to the pane (so the
  // pane transitions to ChatPane and subscribes to the stream), then invokes the
  // skill — mirroring the text-send transition. Doing the skill invoke locally
  // (without the pane assignment) left the landing pane stuck/blank.
  const handleSlashCommand = useCallback((skillName: string, userMessage: string) => {
    onSkillInvoke(skillName, userMessage.length > 0 ? userMessage : null);
  }, [onSkillInvoke]);

  const restoreAndOpen = useCallback(async (id: string) => {
    try {
      await onUnarchiveChat(id);
      onOpenChat(id);
    } catch {
      // onUnarchiveChat surfaces its own toast.
    }
  }, [onUnarchiveChat, onOpenChat]);

  const openChats = [...chats.filter((c) => c.status === 'open')].sort(byRecent);
  const openIds = new Set(openChats.map((c) => c.id));
  const archivedChats = archived.filter((c) => !openIds.has(c.id)).sort(byRecent);
  const isEmpty = openChats.length === 0 && archivedChats.length === 0;

  return (
    <div className="flex flex-col h-full min-h-0">
      <div className="flex-1 min-h-0 overflow-y-auto">
        <div className="max-w-[760px] mx-auto w-full px-4 py-4">
          {isEmpty ? (
            <p className="text-sm text-muted-foreground text-center py-8">
              No conversations yet. Send a message to start.
            </p>
          ) : (
            <>
              {openChats.length > 0 && (
                <>
                  <h3 className="text-xs font-medium uppercase tracking-wide text-muted-foreground px-1 mb-1.5">
                    Conversations
                  </h3>
                  <div className="space-y-0.5 mb-4">
                    {openChats.map((c) => (
                      <button
                        key={c.id}
                        type="button"
                        onClick={() => onOpenChat(c.id)}
                        className="w-full flex items-center gap-2 text-left px-2 py-1.5 rounded hover:bg-muted text-sm max-md:min-h-[44px]"
                      >
                        <MessageSquare size={14} className="shrink-0 text-muted-foreground" />
                        <span className="truncate shrink-0 max-w-[45%]">{c.name ?? 'New chat'}</span>
                        {c.last_message_preview && (
                          <span className="truncate flex-1 text-xs text-muted-foreground hidden sm:block">
                            {c.last_message_preview}
                          </span>
                        )}
                        <span className="shrink-0 ml-auto text-xs text-muted-foreground">
                          {formatRelative(c.updated_at)}
                        </span>
                      </button>
                    ))}
                  </div>
                </>
              )}
              {archivedChats.length > 0 && (
                <>
                  <h3 className="text-xs font-medium uppercase tracking-wide text-muted-foreground px-1 mb-1.5">
                    Archived
                  </h3>
                  <div className="space-y-0.5">
                    {archivedChats.map((c) => (
                      <button
                        key={c.id}
                        type="button"
                        onClick={() => void restoreAndOpen(c.id)}
                        title="Restore and open"
                        className="group/arch w-full flex items-center gap-2 text-left px-2 py-1.5 rounded hover:bg-muted text-sm text-muted-foreground max-md:min-h-[44px]"
                      >
                        <Archive size={14} className="shrink-0" />
                        <span className="truncate flex-1">{c.name ?? 'New chat'}</span>
                        <span className="shrink-0 text-xs">{formatRelative(c.updated_at)}</span>
                        <RotateCcw
                          size={13}
                          className="shrink-0 opacity-0 group-hover/arch:opacity-100"
                        />
                      </button>
                    ))}
                  </div>
                </>
              )}
            </>
          )}
        </div>
      </div>
      <ChatInput
        disabled={false}
        projectId={projectId}
        sessionId={sessionId}
        agentId={agentId ?? null}
        onAgentChange={onAgentChange}
        onSend={handleSend}
        onSlashCommand={handleSlashCommand}
        chatId={chatId ?? undefined}
        chatLabel="Chat"
        messages={[]}
        modelContextLimit={null}
      />
    </div>
  );
}